I have wifi thermostats.

If you would like, I can search for possible remedies or components that can be replaced within the fridge (circuit board, thermostat, etc), though the unit is 17 years old and I'm not sure what parts may still be available."

The full service option typically charges 15-25% of rental income, possibly a monthly fee and provides all services needed, bookings, guest check ins, guest complaints, maintenance, housekeeping, inspections and maybe even payment of STR taxes after guests leave.I am more hands on in my rental and have smart devices that make my life a little easier, smart locks, smart exterior lighting, smart thermostat, loud noise indicators and smart smoke detector. 

Our thermostat (Emerson Sensi) sends me details like humidity etc based on preset alerts.

Each floor has separate thermostat there are both on separate breakers one unit is a 3 bedroom the 2nd unit said 2 bedroom

Also control the thermostat yourself.

We installed Ecobee thermostats and had the utility company conduct an energy audit, but there's really nothing else we can do.We are receiving around $2325.00 per unit per month.

Smart Thermostat.

Another way I have handled this in unheated basements is to install a small electric baseboard heater with a thermostat.

We have upgraded the baseboards to hydronic, and upgraded the old mercury thermostats to digital, and added insulation in all areas, which has helped to reduce winter time electric bills, but tenant turnover remains high due to lack of summertime cooling, and high wintertime electric bills (electric bills range from $50 to $400).